1. Field
This invention pertains to methods for increasing the performance for gas turbines and internal combustion (IC) engines. Specifically, it relates to a new multi-stage method and apparatus for cooling the inlet air of gas turbines and internal combustion engines to increase their power output and combustion efficiencies.
2. State of the Art
As described in The Second Law by P. W. Arkins, published by Scientific American Books, Inc., 1984, at pages 102-105 the operation of a turbine is thermodynamically described by the Brayton cycle, which is basically a collection of repetitive sequential energy transfer processes. The compressor stage is generally driven by a gas turbine engine, but it is more appropriate to think of it as an axial compressor which is like a rotating fan of some kind. In this stage, the working gaseous fluid (air) is compressed in a series of compressor blades by a turbine and burning it in the combustor section which then drives the hot gases through the turbine blades and powers them. An interconnecting shaft from the compressor section through the turbine section extends out to drive a generator or pump or other mechanical rotating device.
This compression process is adiabatic, and it raises both the temperature and pressure of the compressed air. After the air is compressed, fuel is added and energy is transferred to a high-temperature, high pressure gas stage (because fuel burns, or because there is some kind of heat exchanger fueled by a hot source). Its temperature then rises still further, but the engine is arranged so that at the same time the volume of the gas is allowed to increase; overall, therefore, the gas remains at constant pressure. The hot, expanded gas then enters the turbine stage where there is an adiabatic expansion of the gas against the turbine blades. This cools the gas and extracts its energy as work resulting from the transformation of the incoherent thermal motion of the hot gas into the coherent rotational motion of the blades of the turbine. The last stage then lowers the gas temperature at constant volume via dumping heat into a sink in order to complete the cycle to achieve a viable engine. The technical difficulty of making this cycle practicable requires hot and cold devices to be separated so that the turbine is kept at a high temperature while it is running.
As a thermodynamic process, it is well known that the performance of a gas turbine or IC engine can be increased by cooling the air inlet to densify the air mass flowing into the engine and into the compressor blades or cylinders. Typically this is accomplished via an evaporative cooler associated with the air inlet stream entering the compressor. This choice is due to the low capital cost to install an evaporative cooler in comparison to that of a refrigerated air system. The turbine performance increase when associated with an evaporative cooler is limited to the ambient wet bulb temperature of the region. In addition, evaporative coolers are wet systems with high maintenance problems associated with scaling. They are also dependent on water availability and price.
Therefore, although an evaporative cooler is workable and economical, particularly in low humidity areas, additional performance can be achieved by a source of constant lower temperature refrigerated inlet air. This is especially the case where the optimum turbine/engine performance is achieved at temperatures below that of the daily fluctuating evaporative cooler wet bulb temperature in an area.
Conventional single stage temperature. refrigeration systems consume considerable energy to reduce the ambient inlet air to the temperature to that required for optimum turbine and engine performance.
The present invention reduces the overall power consumption of the inlet air cooling system by providing an improved multi-stage constant air cooling system method and apparatus for optimizing turbine and engine performance.